The present invention relates to a control unit or controller for a vacuum pump, particularly for a vacuum pump of the turbomolecular type.
As it is known in the art, a turbomolecular vacuum pump comprises a plurality of pumping stages housed within a substantially cylindrical casing and provided with an axial inlet port of the sucked gases located at one end, and with a radial or axial exhaust port of the gases located at the opposed end.
The pumping stages generally comprise a rotor disk, secured to the rotatable shaft of the pump, that is driven by an electric motor at a speed usually not lower than 25,000 rpm and in some cases as high as 100,000 rpm.
The rotor disk rotates within stator rings fastened to the pump casing and defining the stator of the pumping stage, with a very small gap therebetween.
In the space between a rotor disk and the associated stator disk a pumping channel of the sucked gases is further defined.
The pumping channel defined between the rotor and the stator in each pumping stage communicates with the preceding and the subsequent pumping stages through a suction port and an exhaust port, respectively, provided through the stator in correspondence of the pumping channel of the sucked gases.
A turbomolecular pump of the above type is disclosed for example in U.S. Pat. No. 5,238,362 assigned to the Assignee of the present invention.
The turbomolecular pump described in U.S. Pat. No. 5,238,362 employs both pumping stages provided with rotors formed as flat disks and pumping stages provided with rotors equipped with blades.
This combined arrangement of pumping stages allows for a very good performance of the pump for what concerns the compression ratio, while allowing to discharge the gases into the outer environment at atmospheric pressure by means of simple pre-vacuum pumps without lubricant, such as diaphragm pumps.
Moreover, the construction of the vacuum pump of the turbomolecular type as taught by U.S. Pat. No. 5,238,362 allows for a considerable reduction of the pump power consumption.
It is further known to employ electronic control units or controllers for feeding the motor of a vacuum pump in general, and more particularly of the turbomolecular type, equipped with a transformer for converting the available AC mains voltage into the rated voltage level suitable for the operation of the vacuum pump.
Because of the overall size and the cooling requirements mainly caused by the presence of the transformer, the known unit must be mounted separately from the turbomolecular pump and be provided with dedicated cooling devices in addition to those already provided for cooling the pump.
Namely the presence of a transformer in the known control units not only increases the unit size, thus preventing the construction of a compact device that could be integrated with the pump into a single pumping apparatus, but further creates an additional heat source that raises the temperature of the control unit and of the circuitry forming such unit.
In accordance with the known art, this implies the provision of a control unit separated from the vacuum pump, to be independently cooled and electrically connected both to the mains and to the vacuum pump by conductors of suitable lengths and cross sections.
In the field of the vacuum pumps it is further known that the feeding voltage level must be changed during the operating cycle on the basis of the residual pressure within the vacuum pump and the operating conditions of the pump motor from the starting condition to the steady state rotating condition.
Since the feeding voltage level of a turbomolecular pump effects the pumping speed at which the gases are pumped, there have been designed control units of the above described type for vacuum pumps, capable of supplying the vacuum pump with a plurality of voltages that are selected as a function of the pump current, and therefore as a function of the pressure level inside the pump.
In such control units the voltage applied to the motor of the pump can be adjusted, for example through an SCR or a TRIAC controlled rectifying bridge.
On the other hand the voltage level of the mains can be varied, for example, through a transformer having a primary winding divided into a number of sections that are connected to as many switch contacts.